Project Summary The HIV-1 accessory protein Vpu enhances viral infectivity by modulating several host cell proteins that are detrimental to the virus, including CD4 and BST-2 (tetherin), and preventing them from being incorporated into viral particles. Importantly, Vpu activities result in the protection of HIV-1 infected cells from cellular immune responses such as antibody dependent cell-mediated cytotoxicity (ADCC). For this reason, inhibitors of Vpu activity could be used to enhance immune killing of HIV infected cells in patients. This type of inhibitor could be an important component of therapies aimed at eliminating reservoirs of HIV infected cells. The Johnson lab serendipitously discovered that Vpu targets the viral glycoprotein from Gibbon ape Leukemia Virus (GaLV Env) and prevents it from being incorporated into HIV-1 viral particles. Therefore, inhibiting Vpu activity greatly enhances infectivity when HIV-1 is used with this glycoprotein. GaLV Env was selected as a surrogate Vpu target in an assay for identifying inhibitors of Vpu activity. Unlike other types of Vpu assays, the output (infectivity) is quantitative in nature and very amenable to a high throughput screening. Along with collaborators at Southern Research Institute (SRI, see letter of support), a large high throughput screening (HTS) campaign of over 650,000 compounds was initiated using this assay in hopes of finding appropriate Vpu inhibitors that could be advanced to clinical applications. This screen and dose response validation of the hits was completed in August 2017 and identified 205 candidate Vpu-inhibiting compounds. The ultimate goal of this project is develop compounds that can be used to block Vpu activity in a clinical setting. The objective of this proposal is to determine which compounds from the HTS campaign are most suitable for further development as clinical Vpu inhibitors. 1. Conduct hit-to-lead studies to identify the best compound candidates. a. Screen for compounds that do not block cellular SCF Ubiquitin machinery (off target). b. Screen for compounds with Vpu-specific activity. c. Screen with advanced toxicity and ADME assays to identify most desirable compounds. 2. Select for compounds with the desired biological activity. a. Screen for compounds that block Vpu antagonism of CD4. b. Screen for compounds that block Vpu antagonism of BST-2. c. Screen for compounds that directly bind to Vpu.